Chip cards essentially comprise a chip card body, generally a plastic card, which has a space for accommodating the semiconductor chip. This space usually comprises an outer, shallow cavity, in the base surface of which a further, inner cavity is recessed.
The inner cavity has a smaller cross-sectional area than the outer cavity, and consequently the outer cavity extends laterally beyond the inner cavity. The base surface of the outer cavity surrounds the inner cavity.
The inner cavity is used to accommodate the semiconductor chip in the chip card body. The carrier substrate, to which the semiconductor chip is electrically and mechanically connected, is arranged in the outer cavity. The electrical connections between the semiconductor chip and the surface contacts on the top side of the carrier substrate allow the card to be read and, depending on the chip card, allow information to be written to the semiconductor chip as a result of a chip card ATM making appropriate contact with the upper surface contacts.
The carrier substrate is secured to the base surface of the outer cavity and almost completely fills the outer cavity. At the same time, the carrier substrate covers the inner cavity, in which the semiconductor chip is located. Therefore, the semiconductor chip is protected from external influences by the carrier substrate.
There are known chip cards whose carrier substrates for this purpose have surface contacts on their top side, while bonding connections, for example bonding wires, which electrically connect the semiconductor chip to the surface contacts, are secured to the rear sides thereof. To enable the bonding wires to be connected to the rear sides of the surface contacts on the top side of the carrier substrate, the carrier substrate has an opening below each contact.
Furthermore, chip cards in which the carrier substrate also has surface contacts on its underside are known.
The surface contacts are electrically connected to the semiconductor chip and also to the surface contacts on the top side of the chip card. To electrically connect the upper and lower surface contacts to one another, contact-hole lines, known as vias, are produced in the carrier substrate. A via is a preferably cylindrical opening in the carrier substrate, which has a diameter of between 0.1 and 1 mm and extends from the underside to the top side of the carrier substrate, the upper end of the via or contact-hole line often being covered by the upper surface contacts. The cylindrical inner wall of the contact-hole lines is processed in such a way that it is electrically conductive on account of a corresponding metallic or other electrically conductive covering of the inner wall, the contact hole forms an electrical line which runs between in each case one upper and one lower surface contact of the carrier substrate.
The semiconductor chip is connected to the lower surface contacts of the carrier substrate by electrical connections and can therefore be electrically driven through the vias from the top side of the carrier substrate.
A semiconductor chip which is enclosed in a chip card has to be insulated from environmental influences, so that moisture or pollutants which are present in the ambient air do not diffuse into the semiconductor chip. To prevent the internal space formed by the second, inner cavity from coming into contact with the environment, the vias, which are openings which pass through the carrier substrate, may be arranged outside the basic area of the second cavity, on the base surface of the first cavity. Consequently, it is impossible for the ambient air to be exchanged with the air in the interior of the second cavity.
However, even as early as during the production process a microclimate which contains moisture and/or pollutants and in the long term have a harmful effect on the semiconductor chip may become enclosed within the second cavity. Damage to the semiconductor chip from this microclimate cannot be reliably avoided even by means of a paste which covers the top side, facing the cavity of substrate, of the integrated circuit. Pollutants which are present in the microclimate can diffuse through the paste or through interfaces between the paste and the semiconductor chip.